1. Field of the Invention
The present invention relates to a solenoid valve for a water purification system.
2. Description of Related Art
Water purification systems typically include a pump that pumps contaminated water through a filter unit. The filter may contain a reverse osmosis membrane which removes impurities in the water. The water is then stored within a tank and subsequently removed by the end user. Water purification systems range in size from large industrial units to smaller systems that can be installed under the sink of a home.
Residential water purification units typically have a valve that controls the flow of water between the pump and a municipal water source. To more fully automate the purification unit, the valves may contain solenoids which are controlled by a control circuit. The valves typically move into an open position when the control circuit provides power to the solenoid. Most solenoid operated valves require a relatively large amount of current to move the valves from the closed position to the open position. The large current is typically needed to overcome the fluid back pressure exerted on the valve, and the internal air gap within the valve and flux gap. Once the valve is opened, the solenoid does not require the large initial current needed to open the valve. The continual supply of excessive power to the valve, may overheat the solenoid and draw in an unnecessary amount of power. The heat may cause the solenoid to fail, thereby reducing the life and reliability of the valve unit. Additionally, the excessive use of power creates a valve that is costly to operate.
The control circuit of the valve is typically powered by the same transformer that powers the motor of the pump. When the pump is turned on, the motor requires a gradually increasing amount of current to correlate with the increasing speed of the pump unit and the back pressure that is generated by the pump. In a typical water purification system, the solenoid valve and pump unit are activated simultaneously, so that municipal water is pumped to the filter unit. The transformer must pull in an increasing amount of power during the initial state of the pumping cycle to accommodate the constant current requirement of the solenoid valve and the ramping current requirement of the pump motor. The transformer must therefore be built to accommodate the maximum current requirements of both devices. It would be desirable to have a solenoid valve which only requires an initial large current to open the valve and then draws a lower amount of current to maintain the valve in the open position. It would also be desirable to have a solenoid valve that has a decreasing current load requirement that matches the increasing load requirement of the pump motor, so that the power provided by the transformer is approximately a constant value during the entire pumping cycle of the system. Residential water purification systems typically have used an AC powered solenoid valve that is driven by the same transformer that supplies power to the systems other electric al components.
AC powered transformers becomes objectionably noisy if the armature is not in full contact with the core of the solenoid. The noise is created by the variable field strength form the alternating current rocking the armature. It would therefore be desirable to have a control circuit that eliminates the risk of noise by providing a DC holding current.